Yo,
So your turning your motor ON/OFF If this is the case, the motor is near enough at stall when its given full battery power to start the drum spinning. I would advise the use of a speed controller and start the drum up slower than giving it full voltage which will heat the motor up alot. What might be perfect for you is a 30amp Electronize Speed Controller from Technobots would sort that out. Even a 15amp might do it, but would recomend a 30amp to be safe as they can deal with drill motors at stall, not sure on the 15ampers.

Kind Regards,
Mr Stu